It means the DL is registered in the database
Each dl issued by local Polish authorities is registered in the national database. All "licences" obtained illegally, e.g., printed in other countries, are not in the database. When the police finds it out, you have a problem - first, you are detained for a criminal act of forging the license and the investigation commences. If you can`t prove you have a permanent address in Poland, you are arrested for at least 3 months to make sure you don`t run away to avoid the trial. That happened to a workmate of mine 20 years ago - he had an American passport but didn`t have an original Polish licence - we had to bring him some stuff to prison. Offenders face sentences from 3 months to 5 years.